In the prior art there are a number of devices which have been developed to facilitate cable-laying operations. Some of these devices combine two or three of the principal functions which are involved in cable laying, including trenching or otherwise opening a kerf, placing a cable at the bottom of the kerf, and refilling the kerf. However, devices of the prior art have a number of disadvantages and drawbacks.
Some of these disadvantages and drawbacks are experienced most severely when such equipment is used for laying relatively fragile cable of small diameter. Laying fiber optics cable can be particularly troublesome. This invention is particularly concerned with solving such problems, and with laying cable in kerfs of narrow width, such as two inches or less. But the invention is useful for laying cable of various kinds.
Fiber optics cable cannot reliably withstand either excessive vibration or so-called "back bending." Excessive vibration can break fibers and thus diminish or break the fiber optical qualities essential to signal transmission in such cable. Excessive vibration is a particular problem for such cable when it is in firm contact with hard surfaces or edges as may be the case when cable is being directed into a kerf.
Cable damage can also be caused by "back-bending" which occurs when insufficient care is given to the manner in which cable is unwound from a reel or when an excessive length of cable is exposed to various pressures, such as pulling and/or unreeling pressures. After being reeled on a cylindrical reel for a period of time, cable can take a kind of "set" which makes bending in the opposite direction, or "back-bending," harmful. Back-bending can destroy fiber optical qualities at the point of bending.
Various cable-laying systems of the prior art cause such vibration and/or back bending and have shown themselves to be disadvantageous in laying fragile cable such as fiber optics cable.
Among the many prior patents disclosing cable-laying operation are the following:
U.S. Pat. No. 3,203,188 (Evans) PA1 U.S. Pat. No. 3,332,249 (Idoine) PA1 U.S. Pat. No. 3,998,065 (Darnell) PA1 U.S. Pat. No. 4,539,765 (Reece) PA1 U.S. Pat. No. 3,788,575 (Boettcher et al.) PA1 U.S. Pat. No. 3,874,182 (Potter et al.) PA1 U.S. Pat. No. 4,040,261 (Schuck et al.) PA1 U.S. Pat. No. 4,038,828 (Schuck et al.) PA1 U.S. Pat. No. 3,405,533 (Fries) PA1 U.S. Pat. No. 3,926,263 (Frisbee et al.) PA1 U.S. Pat. No. 4,119,157 (Schuck et al.) PA1 U.S. Pat. No. 3,931,717 (Schuck) PA1 U.S. Pat. No. 3,948,059 (Pompa) PA1 U.S. Pat. No. 3,618,237 (Davis) PA1 U.S. Pat. No. 3,363,423 (Davis) PA1 U.S. Pat. No. 3,926,004 (Baylor) PA1 U.S. Pat. No. 4,162,087 (Avrillon)
Many of these patents deal with wide-trenching devices having massive rock wheels which are prone to excessive vibration. Many also have long spans of cable from a remote location or a run of unguided cable extending toward the trench bottom. Such lack of cable control can lead to back-bending and other cable movement which may be deleterious to the cable.
A number of these patents, including those which are used to open a relatively narrow kerf, have vibrating trench cutters. Such vibratory cutters can cause damage to fiber optics cable. This is particularly the case when such vibrating devices are closely adjacent to a guide element or other element in contact with the cable.
Cable guide members are highly desirable for minimizing back-bending, but when such elements are vibrating excessively by virtue of the nature of the kerf digger, cable damage may not be avoidable.
A particular disadvantage of certain apparatus of the prior art, particularly those devices having vibratory trench cutters, is that they are not capable of digging sufficiently deep kerfs unless excessive power is used. And the deeper they dig, the greater the level of excessive vibration with all the attendant problems for fiber optics cable.
To overcome some of these problems, multiple-pass cable laying methods have often been used for laying fiber optics cable. This, of course, makes the cable-laying operations very time-consuming and expensive.
The dominant speed of prior multi-function cable-laying apparatus is slow. This is often due to the problems associated with trench digging. There has been a need in the art for improved one-pass cable-laying apparatus which can move at higher speeds along the ground.
Many devices of the prior art which carry out two or three of the primary cable-laying functions are very large and complex and are difficult to operate and maneuver. There has been a need for a compact and maneuverable one-pass cable-laying apparatus. There has also been a need for a simple and reliable one-pass cable-laying apparatus.
In particular, there has been a need for an improved cable-laying apparatus which preserves the integrity of fragile cable such as fiber optics cable.